The present invention relates to the field of sulphurized olefins and more particularly its subject is a new process for preparing sulphurized olefins which are pale in color, by sulphurization using sulphur and hydrogen sulphide.
Sulphurized olefins are products widely used for sulphurizing catalysts and as additives for lubricants or for elastomers. These products are essentially composed of mixtures of organic sulphides, disulphides and polysulphides.
The person skilled in the art knows of numerous processes for preparing sulphurized olefins or organic polysulphides. A first family of processes consists in reacting a mercaptan and sulphur in the presence of a basic catalyst. These processes, described in the patents FR 2 607 496 and FR 2 630 104, for example, are costly, since they require use of mercaptans, which themselves have to be produced from olefins or from alcohols.
The process described in the patent EP 342 454 for preparing dialkyl sulphides and dialkyl polysulphides from olefins is in fact a two-step process, in which initially an H2S+olefin reaction takes place in the presence of a solid catalyst to form a mercaptan and, secondly, this mercaptan is brought into contact with sulphur and with another heterogeneous catalyst, to form a polysulphide. This process has the disadvantage of requiring two steps in succession (2 different reactors), with elevated temperatures.
Other processes which can give sulphurized olefins have been proposed:
1) The olefin+sulphur reaction in the absence of H2S generally prepares colored products. To avoid this disadvantage, operation in the presence of water, or washing with water, has been proposed, but this creates problems in separation of the aqueous phase and in disposing of the aqueous effluent. Processes of this type are described in the patents U.S. Pat. No. 5,338,468, WO 92/03524, WO 92/00367, WO 97/24416, EP 714 970, EP 714 971 and FR 2 757 534. In all these processes, elevated temperatures are required for good conduct of the reaction. The patent EP 201 197 describes the sulphur+olefin reaction at a temperature of 140 to 180xc2x0 C.
2) The olefin+sulphur+H2S reaction has been described in the patents EP 554 011, EP 889 030, U.S. Pat. Nos. 4,119,549, 4,119,550, 4,191,659 and 4,584,113 and the application JP 11-246518. However, elevated temperatures are required for good conduct of the reactions (usually above 110xc2x0 C. to give significant conversion of the reactants) and/or the pressures mentioned are usually very high.
The new process now found for preparing sulphurized olefins by sulphurization using sulphur and H2S in the presence of solid catalysts provides clear, pale-colored products and has the advantage of requiring only slightly elevated temperatures, generally well below 110xc2x0 C., and of permitting operations at only slightly elevated pressures. In addition, the use of solid catalysts allows very ready separation of the catalyst from the final product; using simple filtration it is possible to reuse the catalysts and to obtain a final product which is stable since it is free from catalysts. This process also allows the reaction to be realized in just one step.
The process according to the invention for preparing sulphurized olefins by sulphurization using sulphur and hydrogen sulphide is characterized in that the reaction is carried out in the presence of a solid acid catalyst and of a solid basic catalyst, in just one step.
There is a very wide range of suitable solid acid catalysts for use according to the invention, comprising, for example, various polymers and copolymers having acid functions and known in the art, such as cation-exchange resins, zeolites of acid character, silica-aluminas, sulphated zirconias or supported heteropolyanions, or a mixture of these.
Non-limiting mention may be made of sulphonated resins based on crosslinked polystyrene (preferably crosslinked with divinylbenzene), acrylic or phenylacrylic resins with free carboxyl groups, resins of phenol-formaldehyde type derived from phenolsulphonic acids, lignosulphonic exchangers, etc. . . . . Resins of this type are available commercially with various names, in particular Amberlite, Dowex, Diaion, Duolite, Levatit, etc. Sulphonated copolymers of styrene with divinylbenzene are most particularly suitable. On the other hand, known copolymers of tetrafluoroethylene with a perfluorosulphonic acid, which have the name Nafion, can be employed advantageously. The solid acid resin is preferably used as dry as possible.
There is a very wide range of suitable solid basic catalysts for use according to the invention, comprising, for example, polymers or copolymers well known in the art and having basic functions, such as anion-exchange resins, zeolites of basic character, an alumina or silica-alumina doped with alkali metals or with alkaline earth metals, or a mixture of these catalysts.
Non-limiting mention may be made of resins based on crosslinked polystyrene, particularly crosslinked with divinylbenzene, acrylic or phenylacrylic resins, acrylic resins crosslinked with divinylbenzene, or resins of phenol-formaldehyde type. These resins bear primary, secondary or tertiary amine, quaternary ammonium, polyethylene polyamine, guanidine or amidine functional groups. Resins of this type are described in the patents FR 2 630 104, U.S. Pat. Nos. 5,786,511, 5,767,229, EP 931 789, U.S. Pat. Nos. 5,726,253 and 5,817,716, for example.
Anion-exchange resins which may be used are commercially available with a variety of names, such as Amberlite, Amberlyst, Diaion, Dowex, Duolite, Levatit, Reillex, etc.
In the case of the resins with quaternary ammonium functions, preconditioning prior to use could prove useful, for example treatment with sodium hydroxide followed by washing with water and drying.
The efficacy of the anion-exchange resins is generally improved if they are used as dry as possible.
The zeolites of basic character which may be used according to the invention are aluminosilicates characterized by a well-defined pore size and a large specific surface area. These may be zeolites of type X, Y or L containing at least 3% by weight of an alkali metal oxide (such as Na2O), and preferably more than 10%. The sodium cation may also be replaced by another alkali metal cation.
The olefins to be used in the process according to the invention may be chosen from a very wide range. They contain at least one non-aromatic carbon-carbon double bond. They may generally be represented by the formula: 
in which each of the symbols for R1, R2, R3 and R4, which are identical or different, represents a hydrogen atom, an aryl radical or an alkyl radical, linear, branched or cyclic, which contains from 1 to 20 carbon atoms and may contain one or more unsaturations and/or aromatic groups and/or OR5, SR5, NR5R6, CN, COR5, COOR5, CONR5R6, SiR5R6R7, Si(OR5)R6R7, Si(OR5) (OR6)R7, Si(OR5) (OR6)OR7, SO2R5, SO3R5, POR5R6, OP(O) (OR5) (OR6), NO2 or halogen groups, and each of the symbols for R5, R6 and R7 denotes independently a hydrogen atom or an alkyl, cycloalkyl or aryl radical optionally containing one or more unsaturations.
Two of the symbols for R1, R2, R3 and R4 may also represent an unsubstituted or substituted alkylene group, that is to say that the carbon-carbon double bond may be included in a ring, for example in cyclohexene, cyclopentadiene, dicyclopentadiene, etc. The olefin of the invention may equally be an unsaturated or polyunsaturated fatty acid, an unsaturated or polyunsaturated fatty acid ester, a derivative of a fatty acid containing at least one double bond, or a mixture of the latter. For example, this compound may be oleic acid, linoleic acid, linolenic acid, palmitoleic acid or their esters of natural origin such as triglycerides or of synthetic origin such as, for example, esters of aliphatic alcohols or polyols. These fatty acids and esters may be used alone or mixed such as in natural fats, oils or fats of vegetable or animal origin, and derivatives thereof. Examples are sunflower oil, soybean oil, colza oil, rice bran oil, castor oil, tallow oil, tall oil, and the like. In the frame of the invention, the natural fats or their derivatives may contain some proportion of saturated acids or esters which act like solvents under the operating conditions of the invention.
The olefin of the invention may equally be a terpene, such as pinene, menthene, limonene, etc.
Mixtures of a number of olefins may also be used. By way of example, mention may be made of the mixture of a natural fat with an unfunctionallized aliphatic olefin.
It is preferable to use an olefin such as isobutylene, diisobutylene, triisobutylene, tripropylene, tetrapropylene, a fatty acid, a fatty ester, a mixture of fatty acids or esters, or an oil of vegetable or animal origin possibly mixed with an unfunctionallized aliphatic olefin.
The olefins used according to the invention may also be diluted in solvents. At the end of the reaction, these solvents are vented or separated by distillation. Examples of solvents of this type are saturated aliphatic hydrocarbons, such as methane, ethane, propane, a butane or a pentane. Using mixtures of this type made from olefins and saturated hydrocarbons can substantially improve the cost-effectiveness of the process according to the invention, in that starting materials of this type can be less costly than a relatively pure olefin-starting material. For example, it is possible to use a cut comprising saturated and unsaturated hydrocarbons having 4 carbon atoms in place of pure isobutylene.
The sulphur may be used in solid form, as pastilles, powder or in liquid form. The sulphur/olefin molar ratio may be from 0.4:1 to 2.5:1, preferably between 0.5:1 and 2:1.
The H2S/olefin molar ratio may vary over a wide range (from 0.5:1 to 5:1 or even more), but it is preferable to use the minimum of H2S required for the reaction to work satisfactorily, or an H2S/olefin ratio of between 0.5:1 and 2:1.
The process according to the invention may be worked batchwise or continuously.
The catalytic efficacy of the acid and basic catalysts can generally be seen from a minimum amount of 0.1% by weight of each of the two catalysts with respect to the amount of olefin. In most cases, the maximum useful amount is of the order of 30% by weight for each of the two catalysts. In a batch process the preferred amount is between 5 and 20% for each of the two catalysts.
When the process is worked continuously, one charge of catalyst may be used over long periods for preparing large amounts of product, and the catalyst/olefin ratio by weight is no longer of great significance.
The relative proportion of the two catalysts may vary widely. The acid catalyst/basic catalyst ratio by weight generally used is between 1:10 and 10:1, preferably between 1:2 and 2:1.
The process according to the invention may be worked in any appropriate equipment, for example in a reactor equipped with a stirrer, where the catalysts are in suspension in the liquid reaction medium. It may also be worked using a tubular reactor in which the catalysts are arranged in a fixed bed, in a moving bed or in an expanded bed; in this case, the acid catalysts and basic catalysts may be used mixed or in alternating layers.
The reaction itself may take place over a wide range of temperature, according to the olefins used and the type of catalysts employed. It is generally carried out at a temperature between 0 and 160xc2x0 C., preferably between 0 and 110xc2x0 C., more preferably between 20 and 90xc2x0 C.
The reaction is conducted at a pressure appropriate to the conversion of the olefin. Operations are advantageously carried out at between 1 and 50 bar absolute, preferably between 1 and 20 bar absolute. The pressure may vary during the course of the reaction, particularly as a function of the temperature profile and of the progress of the reaction.
After a phase under pressure in a closed reactor where the olefin is converted, it is advantageous for the reactor head space to be set to atmospheric pressure or to subatmospheric pressure, so as to remove excess H2S and to complete conversion of the mercaptan formed. In this latter phase an inert gas may be introduced (for example methane, air or nitrogen) so as to entrain the residual volatiles, such as H2S, or the residual olefin.
In the case of a batch reaction, at the end of the reaction the mixture of catalysts may be reclaimed by simple filtration and reutilized.
If it is desired to reduce the odor of the product, or to stabilise the same or reduce its corrosivity, the sulphurated product may be treated by any method known to the person skilled in the art. Methods of this type are described in the patents JP 58140063, U.S. Pat. Nos. 5,155,275, 5,206,439, 5,218,147, 5,403,961, 5,457,234, 5,530,163, 5,559,271, 5,091,112, 5,174,922, 5,208,382, 5,242,613, EP 76376 and EP 933 358 for example.